Input and output coaxial-type circuits for double ended vacuum tubess



June 24, 1953 L. KOROS ET AL 2,840,647

INPUT AND OUTPUT COAXIAL-TYPE. CIRCUITS FOR DOUBLE ENDED VACUUM TUBES Filed May 23, 1956 3 Sheets-Sheet 1 IN VEN TOR.

0 LESL/E L. Kafias 1 MEAZE M H00 VE-f? (Wm 00E f 5 1 42, I (6490mm) mm A/7' Ml jg sown MM W475? 0417f IrTOK/VEY n 1958 L. L. KOROS ETAL 2,840,647

INPUT AND OUTPUT COAXIAL-TYPE C UITS FOR DOUBLE ENDED VACUUM TU Filed May 25, 1956 5 Sheets-Sheet 2 Ill l r a f3 1554/5 4.595522% ER'LE Haws/7 OUT/ 07m June 24, 1958 L. L. KoRos ET AL 2,840,647

INPUT AND OUTPUT COAXIAL-TYPE CIRCUITS OR DOUBLE ENDED VACUUM TUBES Filed May 23, 1956 3 Sheets-Sheet 3 R5 K33 MV. AM

1C6 Patented June 24, 1958 INPUT AND OUTPUT COAXIAL-TYPE CIRCUITS FOR DOUBLE ENDED VACUUM TUBES Leslie L, KorospCamden, N, 3., and Merle V. Hoover, Lancaster, Pa., assignors to Radio Corporation of America, a corporation of Delaware Application May 23, 1956, Serial No.'586',690 12 Claims. Cl. 179-171 This invention relates to an improved arrangement'of input and output circuits for double ended vacuum tubes, that is, vacuum tubes such as triodes or tetrodes constr'ucted so that they may be physically and electrically inserted at axially or longitudinally intermediate points in coaxial line input and output circuits-or cavities.

At very high and ultra-high frequencies, such as from about lSO rnegacycles to 1000 megacycles, it is difficult to construct high power vacuum tube circuits because certain' ,physical dimensions necessarily related to the operating Wavelength are small. The smallphysical dimensionslimit the capacity of the tube and the associatedcircuits to handle high powers without voltage breakdown. 7 v

Another limitation at the high frequencies results from the fact that an appreciable portion of an electrical wavelength exists within the vacuum tube envelope. For example, when a coaxial line input circuit is coupled to the cathode and grid electrodes of the vacuum tube, the physical lengths of the cathode and grid electrodes may be a substantial portion of a quarter wavelength at the operatingfrequency. Therefore, when the input circuit istuned to resonance, the electrodes at one end have maximum signal voltage thereacross and at the other end have a relatively low signal voltage thereacross. Thus, the electrodes are relatively inactive at one end. The foregoing difficulties may be overcome by employing a double ended vacuum tube wherein a central cylindrical cathode is surrounded by a cylindrical control grid which is in turn surrounded. by a' cylindrical anode. A double ended tetrode may be employed having a cylindrical vscreen grid between the control grid and the anode. Electrode contact rings are connected from both ends of each cylindrical electrode to thee terior of the vacuum envelope. The large cylindrical surfaces of the electro des p'rovide correspondingly large power handling capacity while maintaining small dimensions between the electrodes.

The cylindrical configuration of the electrodes and the electrode contact. rings at bothends of each electrode permit the cathode and grid electrodes to; beinser't'ed at an axially intermediate point in a coaxial line input circuit, and permit thegrid and anode electrodes to be inserted at an axially intermediate point in a coaxial line output circuit. One end of' the input circuit is terminated-to provide a signal voltage distribution such that a radio frequency voltagefmaximum'exists betweenfthe cathode and grid electrodes at the axial'center of the electrodes, and high radio frequency voltages exist throughout the entire axial length of theelec'trodes. One end of the output circuit is terminated to ,providean optimum signal voltage distribution between the g ri and anode axially along the lengths thereof. I i 7 An object of this invention is to provide an'improved vacuum tube circuit capable of translating very high radio frequency power at high frequencies.

Another object is to provide an improved vacuum tube circuit construction capable of being adjusted fofop- :2 eration' at any. desired frequency over abroad range of 'values. H v A further object is to provide an improv d a num tube'cir'cu'it capable of uniformly amplifying broadband signals such as' television radio frequency; visual signals. A still furt'her ob ject is to provide an; improved double ended vacuum tube circuit construction havingniany advantageouepraictizial features. In one aspect, the invention comprises: a circuit including a double ended vacuum tube'having eatho'de, grid and alone electrodes eons't'ructed and arranged injthe form of progressively larger concentric cylinders Bleetrode contact rings are' c onnected from the ends of e' aeh cylindrical electrode to theexterior of the' vacuum envelope. A coaxial line input circuit is connected tothe grid and cathode electrode contact rings atone end of the vacuum tube, and an open-circuited coaxial line input terminating line or circuit is coupled to thecathode and grid electrodecontact rings at the other end of the vacuum tube. .,The input coaxial line and the; input terminating line are adjusted to provide a signal voltage maximum at the axial center of the cylindrical ca thode an grid electrodes. A coaxial-line output lineor ciran: is coupled to the gridand anode electrode contact rings at one end; of the vacuum tube, and a short-circnited coaxial lineioutput terminating line or circuit is coupled to. the grid and anode electrode contact rings at the other end of the vacuum tube. The outpu tfcoaxial line and the outputterminating lineare adjustedtojprovide a signal voltage maximum at the axial center of the grid and anode electrodes within the vacuum tube. input coaxial line a ndtheoutputcoaxial lineextend from opposite ends of the. double ended vacuum tube. I

These andother objectsand aspects of the invention will be apparent to those skilled in the art fromtheifollowing more detailed description taken in conjunction with the appendedjdrawings, wherein;

Figure 1 isavertical sectional view'of an anipliiier constructed according tothe teachings of this invention; 7 Figure 2' is a transverse sectional view taken on the 1ine2 2 ofFigurel up u H Figure 3 "is a transversesectional view taken on the ofFigure. Figure s a ne d ag am. h 1-W. 9ret efs to in describing the operation "of the ainplifier-shown-in Figures 1 thru 3; and

Figure 5 is a diagramillustrating anlarnplifier togthat shown in Figures 1 thrueB but havingimodified input and output terminating circuits. I j 1 Referring now in greater detail to the amplifier shown in Figures 1 thru 3 of the drawings, wherein all-- parts are figures of revolution, theamplifier includes adouble ended vacuum tube designated it) having, at the input endof the tube, a cathode contact ring ll, a grid contact ring 12, and an anode contactring 13; andhavirig at the output end of the tube, a'cathode contact ring- 14, .a gridcpntact ring 15, and an anode contact ring. The anode contact rings 13 and 16 are actually two parallel surfaces of a single metallic structure. variouselectrode contactringsare separated by means of ceramic portions 69 defining the vacuum envelope.

Thedouble ended vacuum tube 10 may be an, RCA lype-A-23 3 5 vacuum tube which is described in patent applicationSerial'No. 534,971, filed by Lloyd P. Garner on September-1 9, 1955; and assigned to theassignee of thepresent application. The electrodes within the vacuurn envelope are arranged in the form of concentric cylinders. An innermost cylindrical filamentary eathode is drical form surrounding thegridelectrode. The ends of the cylindrical anode electrode are efiectively connected to thea node contact rings 13 and 16. The double ended vacuum tube construction is generally .similar to that shown in Figure. l of Patent No.. 2,591,963 issued on April 8 l952,'to L. S; Nergaard. 7 Since the doubleended vacuum tube per se is not our invention, and since our inventioncan be understood with'a general understanding of the doubleended vacuum tube, it is unnecessary to here describe theconstructional details of the tube.

1 Radio frequency'energy is applied to the input electrodes ofthe'vacuum tube 10 by means of an input lineincluding an inner conductor 20 connected by means of spring fingers to the cathode contact ring 11 and an outer conductor 21 connected by means of spring "fingers tothefgrid contact ring 12. An annular shorting 'plunger22 'between theconductors 20 and 21 defines one end'ot a coaxial input cavity or circuit designated 23. Thepo'sition of'the shorting plunger 22 is adjusted by meanso f a rod 24. The shorting plunger 22 is positioned to provide a three-quarter wavelength input cavity measfrom theshorting plunger22 to'jthe center of the input electrodes" within thevacuum tube 10.

"Radio, frequency input energy is applied to the input circuit23by means of a branch coaxial line including an finner conductor fi and an outer conductor' 26. A sec-. ond coaxial branch line 27,23 is" connected from the input circuit 23 to a swamping'or broadbanding grid resistdr (not'shown); The inner conductors 25 and 27 branch lines are directlyconnected to the innerc'onductor 20.0f the input circuit 23, and the outer eonductors -26 and 27 of the branch lines are-directly connected to the outer conductor 21 of theinput circuit.

inpu't circuit 23 includes an adjustable section des- Y ignatedQQ-of low impedance coaxial line closely adjacent to theinputelectrode contact rings 11 and 12. The quarterw'ave section of low impedance line 30 is consti- 'tuted"infpart}by:anapertured cup-shaped element 31 -which"is axially adjustable by means of a rod 32. The i section 30 of low impedance line acts as an impedance ftransfomier whichpermits high. signal voltage within the terminating li ne or circuit 38 constituted by an inner conductor, 35 connected tothe cathode contact ring 14 and aniouter conductor 36 connected to the grid contact ring Theinner conductor 35 includes two telescopparts so that the'axial length of the'inner'conductor 35 may be adjusted in'accordance with the desired freaseacy bro emion. An'expansion ring 37 is provided tion' in "which they maybe set.

The input terminating line 38 constituted by the cylin- "oonductors 35 and 36 isopen-circuited at the end. :Hie' telescopinginner conductor 35'is adjusted in length to the open circuit termination at a point 'one-half wavplength from the axial center ofthe cathode and grid electrodes within the vacuum tube 10. Although the 'outielbondtitor u of the input terminating line continues mask the" two .telescoping'sections into any relative posieuit tii bedefseribeiho energy from the input terminating line is propagated beyond the end of the inner i the cut-off frequency. However, a circular partition 39 jun-ma constitutes 'an'inner conductor for the output circonductor flf Energy is not; propagated becauseYthe is fixed'at any convenient location to prevent the propagation of higher harmonics of the carrier frequency which may be present. It may be seen that the dimension of the input terminating line 38 parallel to the longitudinal axis of the tube is small compared to the similar dimension of input transmission line 23.

An output circuit generally designated 40 is constituted by an inner conductor 41 connected to the grid contact ring 15, and an outer conductor 42 connected to the anode contact ring 16. The end of the output cavity or circuit 40 remote from the vacuum tube 10 is terminated by means of an annular shorting plunger 43 adjustably positioned by means of a rod 44. Radio frequency energy is taken from the output circuit 40 by means of a branch coaxial line including an inner conductor 45 connected to the inner conductor 41 of the output circuit, and an outer conductor 46 connected to the outer conductor 42 ing spring fingers engaging the inner conductor 41 of the output cavity, an outer conductive sleeve 53 having spring 'fingers engaging the outer conductor 42 of the output cavity, and a generally cylindrical insulating dielectric member 54 positioned between the sleeves 52 and 53. 'The insulating cylinder 54 may be'constructed of Teflon,

a trade-name for tetrafluoroethylene, or it may be constructed of a ceramic dielectric material having a low radio frequency loss factor. The section of low impedance line has an axial dimension of approximately a quarter-wavelength at the operating frequency, and the low impedance line section'is positioned in the output cavity 40 near the vacuum tube 10 to provide an impedance transformation such that high radio frequency signal voltagesare present between the electrodes within the vacuum tube and relatively low voltages. exist between the inner and outer conductors of the output cavity 40.

The coaxial line output cavity or circuit 40 extends from the shorting plunger 43 thru the low impedance line section 50 and into the vacuum tube 10 thru the grid contact ring 15 and the anode contact ring 16. The cir- "cuitcontinues thru the vacuum tube 10 between the grid andj'anode electrodes therein and emerges from between the grid contact ring 12 and the anode contact ring 13 to an'output terminating line or circuit designated 55. The output terminating line 55 is a radial line constituted by a square, transverse, apertured conductive plate 56, couin Figure 2, is adjusted by means of four arcuate shorting strips 58 operated in unison by a knob '59 and four rods 59. Peripheral walls 57' prevent the escape of radio frequency energy. The output terminating line or cavity 55 thus consists of a radially extending transmission line having four arcuate shorting strips 58 which may be positioned to determine the electrical length of the output terminating lines The electrical field conditions within the output terminating line 55 are complex and ditficult to analyze, but the effect of the terminating line is to provide a short circuit at a desired distance from the axial center of the grid-anode region within the vacuum tube 10. The short circuit termination is provided at a point a quarter wavelength (or three-quarters wavelength) removed from the axial center ofthe vacuum tube electrodes so that a voltage maximum exists at the desired central region within the active portion of the vacuum tube. The output terminating line 55 constructed as shown and described is eminently satisfactory in electrical characteristics, and is especially advantageous in that it may be conveniently and economically manufactured from flat metal stock. A further practical advantage results from the radial arrangement whereby mechanical interference with the other circuit elements of the ampli fier is avoided. It may be seen that the dimension of the output terminating line 55 parallel to the longitudinal axis of the tube is small compared to the similar dimension of output transmission line 40.

A coolant such as water is'applied to the anode of the vacuum tube thru a pipe 60. The water is discharged from the tube thru a pipe labeled Water Out. It will be noted that the arrangement for applying coolant to the anode of the vacuum tube does notin any way'interfere with the circuitry surrounding the vacuum tube. Coolant for other electrodes ofthe vacuum tube is inserted between a pipe 63 and'a' concentric pipe 64; This coolant emerges from the vacuum tube thru the interior of the pipe 64; The pipes 63 and64 also serveto carry filamentburr'ent supplying thefilamentary cathode within the vacuum tube 10. The cathode'contact ring 11 is directly connected to the pipe 63. The inner conductor '28 of the input circuit 23 is connected to thecathode contact ring 11 of the vacuumtube' and is also con} nected to ground. The directcurrent potentials for the amplifier include a 13+ potential having an "order of magnitude of "+10,000 volts with" respect to ground connected 'to'the anode of 'the vacnum tube 10, and a'negativepotential with 'res'pectto ground of about ''60 volts connected to" the grid contact ring 12 thru the outer the input "circuit 23. Mostfof the {circonductor 2 1 cuit'ry'is thus-a high directcurrent potentials with respect to groundandniust' be enclosed to prevent accidental contactbytheoperatorl Several direct current blocking and radio frequency by-passing' capacitors 66 are required inthe amplifier. These capacitors are constructed "by compressin'g' afrustroconicalpiece of dielectriematerial between tapered mat ing edges of the cylindrical c'ori'ductors.

' Reference will ow be made to the line diagram'of Figure 4 for "an explariation'ofthe'operation of the amplitier of Figures l thr'u 3'. "Thefdiagram 'of' Figure" 4' is representative-of the" structure shown in Figure land includes diagonal cross-hatching of the spaces in'com'rnunicatioh with"the" input coaxial line-25, '26, anddifierent diagonal cross-hatching of the'spaces' in communication withthe'output coaxial line 45,46. The "same reference numerals are used to identify corresponding elements in Figureslthru4. a

' The spacein cor'nmunicat'ionwith the input coaxial llne Z5, 26 willbe'see'ir to extend from'th'e shorting plunger 22, thru' the quarter wave section30 of low'impedance line, thru the ceramic s'eal69 'betwec'nthe cathode contacting '11 and the grid'contact ring 12'to the interior of the vacuum tube 10, thence thru the space between the cathode70 and the gridf7l, and out of the vacuum tuoe between-the cathode "contact 'ring" 14 and the'gridcon'tact ring 15 to'theinput terzniuating line 38which' terminates in ari'open circuit.- "The-standing wave voltage distribution in'the' input circuit-path describedis plotted Ontheleft hand chart in Figure'4. It will be seen that the vo1tage at the shorting plunger "22 iszero, that the voltage between the'cathode 70 and the grid 71 within the vacuum tube is high throughout the axial length of the electrodes, and th'at'the voltage at the open circuited end of theinputtermin'ating line 38 is moderately highf Thequarter wavelength'section 3 0 of'low impe'd'anceliiie provides an impedance and voltage t'ra'nsformatio'n'between the tube 10 and theinput "circuitifi' so thatthe signal standing wave voltage inthe input circuit is of moderate value. The loadedQof '6 the input circuit 23 is low, and therefore the input circuit possesses broadband characteristics.

The space in communication with the output coaxial line 45, 46 will be seen from reference to Figure 4 toextend from the shorting plunger 43 in the output cavity 4s), thru the low impedance section 50 in the output cavity 46, thru the vacuum seal 69 between the-grid contact ring 15' and the anode contact ring 16 to the interior of the vacuum tube 10, thence thru the vacuum tube between the grid electrode 71 and the anode electrode 72, and out thru the vacuum seal 69 between the grid contact'ring 12 and the anode contact ring 13 to-the-output'radial terminating line 55. The radial rectangular output terminating line 55 is terminated by a short-circuit provided by arcuate shorting members 58. I

The chart at the right in Figure 4 'illustrates the-volt age distribution at various points along the path described; it will be'noted that the voltage is zero at the shorting plunger 43 'and at the'shorting plunger 58." It will also be noted that the voltage is a maximum within the vacuum tube between the'gridelectro'de' 71 and the anodeelectrode 72. The substantially'quarter wave long section 50 of low impedance'transmissionline providewakvoltage and impedance transformation such that the voltage existing' inthe output circuit 40 is of relatively low value. By this construction, the stored energy in the output circuit 40is kept at alowvalue'with the result that the output 'circuit has broadband characteristics, as required lfor handling television-visual signals, and has goodoperational eflicie'ncy. I

j The amplifierof-Figures lf'thru'4 is adjusted for -oper.- ation at a given frequency as follows: The'telescoping eleine'ht35 is adjusted in length to'provide anopencircuit 1 at "a pointone-lialf wavelengthremovedfromthe axial center 'of the input electrodes within the vacuurn tube. (All dimensions 'h'eiein are given in termsof electrical wavelengths in'th'e -circuit, rather than infree'spacek) Thisinsure's-that a voltage-maximum'exists at the axial center within'the vacuum tube betweenthe'ca'thode :70 and the'grid 71. As a second step, the shorting'plunger Eat the end'of the input circuit-23 i's'positioned 'at a point such that it is approximately three quartersbf a wavelength from the axial center of the -vacuum-'tube=10. The adjustable cup-shaped member 31 defining the length and position of the low impedance'transmission *line'se'ction 30 is then adjusted axially to the position FatWhich maximum gr'id'current is'obtained, Afterthist adjustment is made, the electrical length from the center of'the vacuu'rn'tube to the tuning plunger 22 is exactly threequarte'rs of a' wav'elength. i 1 Now referring to theoutput circuit, the shorting members 53 in the output terminating 'line'55are= positioned a quarter-wavelength removed from-the axial' c'nter or the vacuum tube. Thisinsur es' a voltage maximum within the vacuum tube atthe axial center of the'gri'd electrode 71"and the anode electrode 72.. The quarterwave sectionSOof low impedance line' is then positioned so that approximately a half-wavelength exists between the loadcn'do'f'thesectionetland theaxialcenter of the grid and anode electrodes within thevacuum:tube;* Then the shortingplunger 43 is axially positioned-to provide a proper impedance match-between the output cavity 40a'nd the output coaxial line 45, 46, andthc desired broadband characteristics. Figurefiis a diagram illustrating-an amplifier similar to that shown inFigures '1 thru'4j but'havinga modified inputterminating line SSand a modified outputtermi nating line 55' which differ in construction compared with the corresponding terminating lines=38 and 55,respectively, in Figures l=thru'- 4. The telescoping inner conductor 35' of'the input terminating line'38' *is' provided witha' circular conductive closure or wall 801 "A circular shorting plunger 81 is provided'wi'th spring fingers around its periphery which engagetheouter conductor 36' of the.inputterminatingline 38. The shortingplunger 81.,isoperatedby a rod 82. By this construction, the input terminatingline 38' is in the form of a coaxial line 35', 36. which terminates inan inwardly directed radial transmission linc formed by circularmembeta. 80 and 81.. .Theradial. transmission line is opencircuited at the axial center. The input terminating line 38. is adjusted so:.that the axial center of the radial transmission lineportion .is moved from the axial center of the vacuum tube an electrical-distance equal to a multiple of half-wavelengths at the operating frequency. The diameter. of the outer conductor 36 is selected to constitute a waveguide which will propagate energy atthe operating frequency...

The output terminating line 55' in the embodiment of Figure diflers from that shown in Figures 1 thru'4 in that thelineis of coaxial line configuration rather than radial configuration. It will be understood that one or both of the modifications illustrated in Figure S'may be incorporated in the amplifiershown in Figures 1 .An amplifier in accordance with Figures 1 thru 3 of the drawings was constructed for operation as the final stage of'a U. H. F. television broadcasting transmitter. -The-amplifier. was. dimensioned for operation between 450 to 150 megacycles, and was tuned to;540 megacycles. A six kilowattinput signal was amplified to provide an output of ll0kilowatts with acontinuouswave signal, and during another experiment, 200 kilowatts at the peak of syncotatelevisiongsignal. ,Witha B+ voltage of 10,000 'volts, the amplifier uniformly amplified frequencies within a 12 megacycle bandwidth. The quarter wave section 50 .of low impedance transmission line in the outputcircuit 40 had an axial length of 3.35 inches. The dielectric'sleeve. 54 wasconstructed of Teflon and had a mean diameter of 7.22 inches. The input terminatingline 38 had a diameter of about 6 inches, This dimensionis such that radiofl frequency energy below 1,170 megacyclescannot be propagated thru the circular waveguide constituted by the outer conductor 36. Therefore, no additional structurewas needed to insure an open. circuit termination at the end of the telescoping inner conductor 35. The dimensions of the various coaxial line conductors in the amplifier were such that the input line 25, 26 had a characteristic impedance of 50 ohms, the input cavity 23 had a characteristic impedance of about 40 ohms, the quarter wave section 30 had a characteristic impedance of about 4 ohms, the. output circuit 40 had a characteristicimpedance of about 35 ohms, the low-impedance section 50 had a characteristic impedance of about 3 ohms, and the output transmission line 45, 46 out beyond the tapered section had a characteristicimpedance of 75 ohms.

As shown in Figure 1 of the drawings, the input and output circuit construction is such as to permit the flow of cooling air past all structuralcomponents at which excessive temperatures could cause failure. Air is directedunder moderate pressure. into the cavities near the anode contact ring of the vacuum tube from which the air flows thru the various spring contacts and thru the lines to the exterior of the equipment. The air flows past the quarter wave sections 30 and 50 and out past the shorting plungers 22, 43, and 58. The provisions for directing a coolant such as water thru the vacuum 'tube 10 have previously been described.

It is apparent that according to this invention there is provided an improved vacuumtube circuit capable of handling very high power at very high frequencies.

. What is claimed is:

1. A vacuum .tube circuit comprising a vacuum tube including cathode, grid,. and anodeelectrodes generally arranged in. the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said cathode and grid electrodes, respectively, an input terminating line having inner and outerconductors coupled at one end to the otherends of said cathode and grid electrodes, respectively, the other end of said input terminating line being terminated to provide a voltage maximum between the cathode and grid electrodes in said vacuum tube at the axial center of said electrodes, an output transmission line having inner andouter conductors coupled at one end to one end of said grid and anode electrodes, respectively, and an output terminating line having first and second conductors coupled at one end to the other end of said grid and anode electrodes, respectively, the other end of said output terminating line being terminated to provide a voltage maximum between the grid and anode electrodes in said vacuum tube at the axial center of said electrodes.

2. A vacuum tube circuit comprising a vacuum tube including first, second, and third electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said first and second electrodes, respectively, said input transmission line including a quarter wave section of relatively low characteristic impedance, an input terminating line having inner and outer conductors coupled at one end to the other ends of said first and second electrodes, respectively, the other end of said input terminating line being terminated to provide a voltage maximum between the first and second electrodes in said vacuumlube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one end to one end 1of said second .and third electrodes, respectively, said output transmission line including a quarter wave section of relatively low characteristic impedance, and an output terminating line having first and second conductors coupled at one end to the other end of said second and third electrodes, respectively, the other end of said output terminating line being terminated to provide a voltagemaximum between-the second and third electrodes in said vacuum tube at the axial center of said electrodes, said input transmission line and said output transmission line being arranged to extend from opposite ends of said vacuum tube.

3. A ,vacuum tube circuit comprising a vacuum tube including cathode, grid, and anode electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said cathode and grid electrodes, respectively, said input transmission line including a quarter wave section of relatively low characteristic impedance, an input terminating line having inner and outer conductors coupled at one end to the other ends of said cathodeand grid electrodes, re-

spectively, the other end of said-input terminating line being terminated to provide a voltage maximum between the cathode and grid electrodes in said vacuum tube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one end to one end of said grid and anode electrodes, respectively, said output transmission line including a quarter wave section of relatively low characteristic impedance, and an output terminating line having first and second conductors coupled at one end to the other end of said gridand anode electrodes, respectively, the other end of said output terminating line being terminated to provide a voltage maximum between the grid and anode electrodes in said vacuum tube at the axial center of said electrodes. i

. 4. A vacuum tube circuit comprising a vacuum tube including first, second, and third electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to'one end of said first and second electrodes, respectively, said input transmission line including a substantially quarter wave long section of relatively low characteristic impedance, an input terminating line having inner and'outer conductors 9 a coupled at one end to the otherends of said first and second electrodes, respectively, theotherend of said input terminating line being terminated to provide a voltage maximum between the first and second electrodes in said vacuum tube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one end to one end of said second and third electrodes, respectively, said output transmission line including a substantially quarter'wave long section of relatively low characteristic impedance, and an output terminating line having first and second conductors coupled at one end to the other end of said secondand third electrodes, respectively, the other end of said output terminating line being terminated to provide a voltage between the second and third electrodes in said vacuum tube at the axial center of said electrodes, the outer conductor of said input terminating line and the inner conductor of said'output transmission line being constituted in part by a common conductive cylindrical wall, the inner conductor of said input terminating line having an end uncoupledfrom the outer conductor thereof to providetan open circuit termination.

5. A vacuum tube circuit as defined inclaim 4 wherein said common conductive cylindrical wall is dimensioned to constitute a waveguide havingia cut-01f frequency higher than the operating frequency of said circuit.

6. A vacuum tube circuit comprising'a vacuum tube including first, second, and third electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said first and second electrodes, respectively, said input trans mission line including a substantially quarter wave long section of relatively low characteristic impedance, an input terminating line having inner and outer conductors coupled at one end to the other ends of said first and second electrodes, respectively, the other end of said input terminating line being terminated to provide a voltage maximum between the first and second electrodes in said vacuum tube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one end to one end of said second and third electrodes, respectively, said output transmission line including a substantially quarter wave long section of relatively low characteristic impedance, and a radial output terminating line having first and second parallel apertured conductors coupled at said apertures to the other end of said second and third electrodes, respectively, the peripheral edge of said output terminating line being terminated by radially movable arcuate shorting elements to provide a voltage maximum between the second and third electrodes in said vacuum tube at the axial center of said electrodes.

7. A vacuum tube circuit comprising a vacuum tube including first, second, and third electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said first and second electrodes, respectively, said input transmission line including a quarter wave section of relatively low characteristic impedance, an input terminating line having inner and outer conductors coupled at one end to the other ends of said first and second electrodes, respectively, the other end of said input terminating line being terminated to provide a voltage maximum between the first and second electrodes in said vacuum tube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one end to one end of said second andthird electrodes, respectively, said output transmission line including a quarter wave section of relatively low characteristic impedance, and a radial output terminating line having first and second parallel apertured conductors coupled at said apertures to the other end of said second and third electrodes, respectively, the peripheral edge 7 line having inner and outer conductors coupled at one '10 of said output terminating line being terminated by radi allymovable arcuate shorting elements to provide a voltage maximum between the second and third electrodes in said vacuum tube at the axial center of said electrodes, the outer conductor of said input terminating line and the inner conductor of said output transmission line being constituted in part by a common conductive cylindrical wall, the inner conductor of said input terminating line having an end uncoupled from the outer conductor thereof to provide an open circuit termination.

' 8. A vacuum tube circuit comprising a vacuum tube including 'first, second, and third electrodes generally arranged in the form of progressively larger concentric cylinders; an input. transmission line having inner and outer conductors coupled at one end to one end of said first and second electrodes, respectively, said input transmission line including a quarter wav'e section of rela} tively low characteristic impedance, an input terminating end to the other ends of said first and second electrodes,

respectively, the otherend of'said input terminating line being terminated as an inwardly extending radial trans: mission line to provide a voltage maximum between the first and second electrodesin said vacuum tube at the axial center of said electrodes, an output transmission line having inner and outer conductors coupled at one 'end toone end of said second and third electrodes, res'pec1 tively, said output transmission lineiinclukling' a quarter wave section 'of relativelylow characteristic impedance, and an output terminating line having first and second conductors coupled at one end to the other end of said second and third electrodes, respectively, the other end of said output terminating line being terminated to pro-- vide a voltage maximum between the second and third electrodes in said vacuum tube at the axial center of said electrodes.

9. A vacuum tube circuit comprising a vacuum tube including cathode, grid, and anode electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said input electrodes, respectively, a cathode and grid terminating line having inner and outer conductors coupled at one end to the other end of said input electrodes, respectively, the other end of said cathode and grid termi nating line being terminated by an open circuit positioned to provide a voltage maximum between said cathode and grid electrodes at the longitudinal center thereof, said open circuit termination being formed by terminating said inner conductor and extending said outer conductor, said outer conductor having a diameter dimensioned to constitute a waveguide which will not propagate at the operating frequency of the vacuum tube circuit, an output transmission line having inner and outer conductors coupled at one end to one end of said output electrodes, respectively, and a grid and anode terminating line having first and second conductors coupled at one end to the other end of said grid and anode electrodes, respectively, the other end of said output terminating line being terminated to provide a voltage maximum between said grid and anode electrodes at the longitudinal center thereof.

10. A vacuum tube circuit comprising a vacuum tube including cathode, grid, and anode electrodes generally arranged in the form of progressively larger concentric cylinders; an input transmission line having inner and outer conductors coupled at one end to one end of said input electrodes, respectively, a cathode and grid terminating line having inner and outer conductors coupled at one end to the other end ofxsaid cathode and grid electrodes, respectively, an output transmission line having inner and outer conductors coupled at one end to one end of said output electrodes,respectively, and an output terminating line having first and second conductors coupled at one end to the other end of said output .electrodes, respectively, the other end of said grid and anode 11 terminating line being terminated to provide a voltage maximum between said grid and anode electrodes at the longitudinal center thereof, one of said terminating lines beingconeentrically inside oneiof said transmission lines and being terminated by an open circuit at the end of the inner conductor of said one terminating line, the outer con ductor of said one terminating line being dimensioned beyond 'saidopen circuit termination to constitute a nonpropagating waveguide at the'operating frequency of the vacuum tube circuit. 1

11. A vacuum tubecircuit comprising a vacuum tube including first and second electrodes generally arranged in the form of concentric cylinders; a transmissionline having inner and outer conductors coupled at oneend to one end of said first and second electrodes, respectively, and a terminating line having inner'and outer conductors coupled at one end to the other end of said first and second electrodes, respectively, the other end of said terminating line being terminated by ari'open circuit positioned, to provide a voltage maximum between said first cylinders; an input transmission line having inner and outer coductors coupled at one end to one end of said cathode and grid electrodes, respectively, an input terminating line having inner andouter conductors; coupled at one end to the other ends of said cathode and grid electrodes, respectively, the dimension of said terminating line parallel to the axis of said cylinders being'small compared to the similar dimension of said transmission line, an output transmission line having inner and outer conductors coupled at one end to one end of said grid and anode electrodes, respectively, and an output terminating line having first and second conductors coupled at one end to the other end of said grid and anode electrodes, respectively, the dimension of said outputterminating line parallel to the axis of said cylinders being small compared to the similar dimension of said output transmission line.

References Cited in the file of this patent UNITED STATES PATENTS 

